1. Field of the Invention
The present invention relates to an organic electroluminescence (hereafter referred to as organic EL) element and a manufacturing method thereof.
2. Description of the Related Art
Organic EL display devices are luminescence display devices which utilize electric field luminescence phenomenon of an organic compound, and are being put into practical use as compact display devices used in cellular phones and so on.
An organic EL display device is configured by placing organic EL elements in an array, on a substrate. Such organic EL elements allow independent luminescence-production control on a per pixel basis. A typical organic EL display device is manufactured by stacking, on a substrate, a driving circuit, an anode, a luminescence function layer, and a cathode. In the luminescence function layer, one or more of function layers, such as an electron injection layer, an electron transport layer, a hole transport layer, a hole injection layer, and so on, are stacked together with an organic luminescent layer made from an organic compound.
In such a configuration, electric charges are injected to the organic luminescent layer from the anode and the electrode via the hole transport layer, and production of luminescence occurs due to the recoupling of the injected electric charges within the organic luminescent layer.
As an example, the organic EL elements for the respective pixels in the organic EL display device are configured by: providing pixel electrodes (for example, anodes) separated on a per-pixel basis on a substrate; placing a bank which is made from an insulating material and includes apertures each corresponding to one of the pixel electrodes; and forming the luminescence function layer in the apertures of the bank.
The luminescence function layer (particularly, the organic luminescent layer) can be formed though the application and hardening of a functional fluid (ink) including an organic compound having an electric field luminescence-producing function, in the respective apertures of the bank.
When forming the luminescence function layer using a method of applying and hardening ink in the apertures of the bank, it is important that the ink, which becomes the functional film, spreads throughout (in other words, fills) the respective apertures.
If the ink is not sufficiently spread throughout the respective apertures, uneven thickness or breaks appear in the resulting functional film, and thus trouble such as uneven luminescence production or short-circuiting defects occurs in the organic EL device.
Consequently, a well known measure for improving the fillability of ink is a technique in which, in an organic EL display device, the contour of the apertures into which ink is applied is shaped to have beveled corners (for example, patent reference 1: Japanese Unexamined Patent Application Publication No. 2006-119270).
Shaping the contour of the apertures of the bank to have beveled corners makes it easier for the ink, which becomes the luminescent layer, to spread up to every corner of the respective apertures. As a result, the luminescent layer is formed with the desired thickness throughout the entirety of the respective apertures of the bank, and the occurrence of uneven luminescence production or short-circuiting defects is reduced.